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Topic: Transmission shift speeds

in Forum: C3 Driveline Components


Transmission shift speeds

Posted: 7/20/03 7:10am Message 1 of 10
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Royal Palm Beach, FL - USA
Joined: 7/16/2003
Posts: 6
Vette(s): 1981 RED COUPE,RED INTERIOR, 43000 MILES, ALL ORIGINAL.
I have a '81 coupe with the 350 transmission with the locking converter. Does anyone know at what speed should it shift into the lockup.Mine seems to shift at about 30 mph which seems early. Is there any adjustments to this shifting that can be made. I am going to change the fluid and filter and see if that makes any difference. I just bought the car and don't know if it has ever been changed even though it only has 43000 miles on it. |headscratch|


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Transmission shift speeds

Posted: 7/21/03 5:02pm Message 2 of 10
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WEST SENECA, NY - USA
Joined: 12/3/2001
Posts: 2379
Vette(s): 1981 Blue Ice Met. w/pearl ghost flames TKO500 5speed. LS1 Swap 3.45 Dana 44.
FrankD,
I recall that most of the GM cars of that era usually shifted into lockup at around 45 mph. 30 mph seems kinda soon. Does the lockup feature "hunt"/ shift in and out constantly? Or once it's in, it's locked in? Let me know what its doing, and maybe we can figure out a couple ways of fixing it.
Sarge |idea|



GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.
3.54 Dana 44
'69 "N11" Sidepipes
Borgeson Steering Box
Born 8/1981
Sequence #3975




Click here to see more pics of my Vette on CarDomain.


Lifetime Member #26

Transmission shift speeds

Posted: 7/22/03 2:25pm Message 3 of 10
Former Member
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Royal Palm Beach, FL - USA
Joined: 7/16/2003
Posts: 6
Vette(s): 1981 RED COUPE,RED INTERIOR, 43000 MILES, ALL ORIGINAL.
Sarge, thanks for the reply. The transmission seems to hunt around 30-35 mph but once pass that speed it locks in. I don't know much about transmissions , i thought if it was an adjustment problem i would take it to a transmission shop.Could a regular 350 transmission be used instead of the lockup one in the car if i need a new one.
thanks Frankd


Transmission shift speeds

Posted: 7/22/03 6:05pm Message 4 of 10
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WEST SENECA, NY - USA
Joined: 12/3/2001
Posts: 2379
Vette(s): 1981 Blue Ice Met. w/pearl ghost flames TKO500 5speed. LS1 Swap 3.45 Dana 44.
Frank, if the tranny doesn't have a ton of miles on it and shifts ok otherwise I have one suggestion for a quick fix to this annoyance.
Look under the dash and find the Brake switch.
Look for a pink wire w/ black stripe, next to it there is a purple wire. These connect to the Converter Lockup Brake switch.
Get a Rocker switch, lighted or unlighted (mount under the dash or where ever you wish)
Take the pink/black wire and splice the rocker switch in-line of that wire.
When you are just cruzin around town 45mph and below leave the switch off. "No more annoyance."
When you hop on the highway (45mph +), reach down and flip the switch on. This will help keep your fuel economy up. It's basically direct drive, no slippage as with a non-lockup converter.
If you are going to swap out tranny's, a normal TH350 will bolt in place. You CAN'T use a lock-up converter on a normal TH350 and "vise-versa." I would go to a overdrive tranny TH700R4 if you are going to swap out.
Hope this helps. Feel free to ask more questions.
Sarge
|cheers|



GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.
3.54 Dana 44
'69 "N11" Sidepipes
Borgeson Steering Box
Born 8/1981
Sequence #3975




Click here to see more pics of my Vette on CarDomain.


Lifetime Member #26

Transmission shift speeds

Posted: 7/24/03 4:32pm Message 5 of 10
Former Member
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Royal Palm Beach, FL - USA
Joined: 7/16/2003
Posts: 6
Vette(s): 1981 RED COUPE,RED INTERIOR, 43000 MILES, ALL ORIGINAL.
Sarge, thanks for the reply, I will make your modification when i get the car back from the paint shop , it is presently being painted the origional spectra red. The new paint will be clear coat while i think the old was st louis lacquer. The car still has the origional brakes which are a bit soft so my next project will be new brakes.
thanks for a great web site
Frank


Transmission shift speeds

Posted: 2/17/04 10:18am Message 6 of 10
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Joined: 2/12/2004
Posts: 43
I have a similar question, my tranny seems to hunt as well, shifting dang early. When it's cold, it will sometimes slip right back to low, and stay low for a while. When it's hot, sometimes it shifts into second, and then right into third about 3 seconds later, at like 25 mph. I think I'll try the switch method, but geez, is there something serious going on?

Thanks !

oh, BTW, I very well could have a 'ton' of miles on my car, 3rd owner, was told it had 45,000 I think more like 145,000 (didn't worry, good buy).

oh, I have the stock '82 TH700R (right?)

|UPDATED|2/17/2004 10:18:32 AM (AZT)|/UPDATED|



'82 CE

Transmission shift speeds

Posted: 2/18/04 9:24am Message 7 of 10
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WEST SENECA, NY - USA
Joined: 12/3/2001
Posts: 2379
Vette(s): 1981 Blue Ice Met. w/pearl ghost flames TKO500 5speed. LS1 Swap 3.45 Dana 44.
surveyguy,
All '82 vette's came equipped with the TH700R4 overdrives. No 4 spd. sticks offered.
Does the tranny fluid appear to be brownish in color or fairly decent red?
The problem may be the "TV" cable. It may be broke, or binding or possibly out of adjustment.
I can email you the adjustment procedures as written by Haynes auto repair manual or you can stop by an AutoZone or most auto parts stores and pick up a Haynes Manual #24040 (274)- Chevrolet Corvette 1968 thru 1982. Very handy book to have.
Or you may want to have a reputable tranny shop take a look at it, and see what their opinion is. If it's determined that there is a ton of miles on it then I would have it overhauled and beefed up a little. The early 700R4's as you should have, were a little on the weak side. Let us know how things go with your tranny problem.
Sarge |cheers|



GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.
3.54 Dana 44
'69 "N11" Sidepipes
Borgeson Steering Box
Born 8/1981
Sequence #3975




Click here to see more pics of my Vette on CarDomain.


Lifetime Member #26

Transmission shift speeds

Posted: 2/18/04 10:25am Message 8 of 10
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CUYAHOGA FALLS, OH - USA
Joined: 12/2/2003
Posts: 6424
Vette(s): 1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!
For those of you with the 350 or 400 (400 did not have locking convertors, but still have controls) you have the vacuum modulator as well as the cable. The vacuum modulator operates on manifold vacuum. With high vacuum it shifts early, low vacuum shifts later. If the modulator fails it can shift very wrong. It's easy to follow a vacuum line to the trans, and remove the modulator. Apply vacuum to the modulator and see if the inside moves. The inside area is where it goes into the trans when installed. You may need to put a rod in the end if you can't see inside, and the rod will move in and out with vacuum change. If you pull the vacuum line off and you see trans fluid in the vacuum line, the modulator is leaking and is bad. These are very easy to remove and install.

To adjust the cable look where the cable attached to the bracket on the carb end. There will either be a chrome like tab that you depress, or a plastic tab that you can pry up with a small screwdriver to release. These are both on the cable housing. Either way, open the throttle all of the way, pull back on the cable housing away from the carb, and relock by releasing the depressed tab, or pushing on the plastic tab. This will set the shift points.

Yes the lockup converter should lock at about 42 to 47 mph, depending on the year and model trans.
Adjust the cable, and check the modulator first. If you still find the "hunting" objectional, install the switch. This works well around town. On the highway you want it to lock, or you will lose fuel mileage. If you for get to turn it on it will cost you in gas, but won't harm anything.

If you have the 700r4 you must have the torque convertor locked when in overdrive. If it does not lock the heat created in the convertor while in overdrive will overheat the fluid and toast the transmission on a long drive. At best you will damage the fluid. At worst you will completely trash the trans. Due to this I do not recommend the switch for the 700r4, the 200r4, or any overdrive automatic.
If your convertor does not lock for whatever failure causes it not to lock, drive the car in regular drive, not overdrive until you can get the problem repaired. This will prevent the overheating of the fluid, and and resulting damage.

Ken Styer

|UPDATED|2/18/2004 10:25:46 AM (AZT)|/UPDATED|



Transmission shift speeds

Posted: 2/25/04 1:26pm Message 9 of 10
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Joined: 2/12/2004
Posts: 43
Thanks, I'll check the adjustment (I have the haynes as well as the chevy book). The oil is new, but I think it was burnt and the last owner changed just before selling it to me.

Update: Ok, I checked the TV cable, a half inch out of adjustment. Drives alot better. Question: is it going to slip out again? What made it slip? What can you do if it keeps going out of adjustment?

Thanks !!!

|UPDATED|2/25/2004 1:26:09 PM (AZT)|/UPDATED|



'82 CE

Transmission shift speeds

Posted: 2/25/04 3:53pm Message 10 of 10
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CUYAHOGA FALLS, OH - USA
Joined: 12/2/2003
Posts: 6424
Vette(s): 1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!
It's shouldn't slip again. If it does you will need to replace the cable assembly. That is what contains the lock to hold it in place. Why did it slip? Maybe it's worn, maybe someone worked on it who didn't know what they were doing or just goofed, maybe the cable was caught and jerked by something from the road. Lot's of maybe. Who knows. You wouldn't think our Chevys would need to deal with Gremlins, they were AMCs! |laugh|

Ken Styer


in Forum: C3 Driveline Components


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